Coherent anti-stokes Raman scattering (CARS) microscopy has evolved over the past decade as a powerful label-free imaging modality based on intrinsic vibrational contrast. A wide variety of important applications involving CARS microscopy have been demonstrated. These range from imaging lipid droplet biology, imaging axonal myelin in spinal cord injuries and demyelinating diseases, identifying obesity related risks in cancer and atherosclerosis and the rapid detection of pathogens. Moreover, it has been clearly shown that there is a tremendous benefit in combining CARS with other imaging modalities, such as two photon excitation fluorescence (TPEF), second harmonic generation (SHG), and third harmonic generation (THG) in a multimodal imaging and spectroscopy platform to obtain a complete picture of the health of the biological tissue. However, in order to truly extend the benefits of multimodal CARS microscopy to human health, development of a multimodal CARS probe in the form of an endoscope or miniaturized hand held microscope is essential. In fact, significant progress has been made in the development of TPEF and SHG imaging endoscopes and miniaturized microscopes for in vivo imaging applications. For CARS microscopy which involves the pump and Stokes beams for excitation of the nonlinear optical signal, progress towards fiber based endoscopy has been quite slow. The key challenges have been (i) the efficient delivery of the ultrafast pump and Stokes light using optical fibers (ii) efficient fiber based collection of the CARS signal (iii) miniaturization of laser scanning mechanisms and (iv) efficient design of chromatic aberration corrected miniature optics for achieving high resolution CARS images. Past research efforts have focused mostly on overcoming the challenges of fiber based light delivery and collection. In particular, laser scanning and focusing at the sample to generate a CARS image was achieved using standard macro-optics, such as a galvanometric scanner and a microscope objective. Only recently, progress was reported related to the design and modeling and implementation of a fiber scanning based CARS endoscope.
Therefore, it is desirable to develop a miniaturized multimodal CARS endoscope. This section provides background information related to the present disclosure which is not necessarily prior art.